[hlmiii]

So we know what to work with, here ...

Originally Posted by Rekraps

The drone is simple resonance, that is frequency matching caused by natural vibrations of the engine, exhause gas and exhaust pipes.

Vibrations together with their environment. In free air vibration dissipates immediately in all directions, without restriction, whereas in other situations vibration is amplified by any nearby or attached hardware, especially enclosure(s).

Originally Posted by Rekraps

I submit that a simple change in the diameter of the piping, more or less, will eliminate the drone.

Not necessarily. It would merely alter it.

Originally Posted by Rekraps

Eventually it will damage or destroy the integrity of the material to which it impacts.

Only in extreme sympathetic (harmonic) situations.

Originally Posted by Rekraps

Tightening the pipes will not help, wrapping them will only hide or surpress the noise.

No. Damping/wrapping reduces amplitude, which results in reduced audibility. To the extent that the vibration is absorbed by the damping material and becomes heat, it is eliminated as noise.
By itself tightening the pipes might help, BTW, if it reduces amplitude (through making it more difficult for the materials to vibrate).

Originally Posted by Rekraps

In order to make it go away the actual resonance needs to be cancelled.

Not necessarily. Damping and/or other control is the most efficient technique.

Originally Posted by Rekraps

... cancel each other out. ... You would have thought the M team would have considered normal cruising RPM and adjusted the piping size accordingly.

To "cancel" vibration there would have to be a second vibration/resonance of the same frequency(s) and the same amplitude generated and then added exactly 180 degrees out of phase (by some additional hardware) in order to cancel the original resonance. Pretty costly and impractical.
Changing the size/materials/mounting/etc. is what controls the frequency of the resonance ("pitch") and amplitude ("volume").

TMI here, for sure.